An ORL-1 (opioid receptor-like 1) receptor (FEBS Lett. 347, 284-288, 1994, FEBS Lett. 341, 33-38, 1994) was found to be a fourth opioid receptor next to δ, κ and μ receptors in 1994. The ORL-1 receptor has about 60% homology of amino acid sequences with other opioid receptors, but it is clearly distinguished from other opioid receptors in that naloxone, a non-selective opioid receptor antagonist, does not bind thereto (FEBS Lett. 341, 33-38, 1994). The ORL-1 receptor is mainly distributed in a central nerve system broadly, and is expressed in high density especially in a cerebral cortex, hippocampus, hypothalamus, amygdala and spinal cord, though it is also expressed in peripheral organs such as intestine and spleen (Eur. J. Pharmacol. 340, 1-15, 1997, Pharmacol. Rev. 53, 381-415, 2001).
Endogenous ligands for the ORL-1 receptor were identified successively by the research groups in France and Switzerland in 1995, and were designated as nociceptin (Nature 377, 532-535, 1995) and orphanin FQ (Science 270, 792-794, 1995), respectively. Nociceptin has been reported to be a peptide consisting of 17 amino acids, and plays a critical role in central functions such as learning, memory, anxiety and stress (Br. J. Pharmacol. 129, 1261-1283, 2000).
Specifically, it has been reported that injecting a small amount of nociceptin to hippocampus of rats causes learning disorder in water-maze learning test (Eur. J. Neurosci. 9, 194-197, 1997) and the nociceptin receptor knock-out mice are quick in learning acquisition in water-maze learning test as compared to normal mice (wild-type), and that long term potentiation (LTP) in hippocampus of knock-out mouse is enhanced as compared to normal mice (Nature 394, 577-581, 1998). Nociceptin is considered to inhibit memory and/or learning functions. In addition, it has been reported that if nociceptin is administered intraventricularly in rats, the anti-anxiety activity is found to be almost equivalent to diazepam in a behavioral pharmacology test such as a conflict test, a light-dark box test and an elevated plus maze test (Proc. Natl. Acad. Sci. USA 94, 14854-14858, 1997). Further, it has been reported that the sensitivity to stress is enhanced, and the adaptation ability to stress is inhibited in nociceptin knock-out mice as compared to normal mice (Proc. Natl. Acad. Sci. USA 96, 10444-10449, 1999). In other words, nociceptin is considered to have a defensive physiological action against anxiety or stress, and the ORL-1 receptor agonist is likely to show anti-anxiety actions by a completely different mechanism from benzodiazepine compounds.
From the above, it has been reported that a compound having an agonistic and/or antagonistic activity for the ORL-1 receptor, is useful for treating a mental disorder, a neural disorder and a physiological disorder, and in particular for improving anxiety and stress disorders, depression, a trauma disorder, memory loss from Alzheimer's disease or other dementia, epilepsy and spasm symptoms, acute and/or chronic pain symptoms, withdrawal symptoms from drug addiction, control of water balance, Na+ excretion, arterial blood pressure disorder and eating disorder such as obesity and anorexia (publications such as JP-A-2000-26466, JP-A-11-228575, JP-A-10-212290, JP-A-2000-53686, WO00/14067, WO99/29696, EP1122257, JP-A-2001-39974, WO00/08013, WO99/36421, EP0997464, WO03/000677, WO98/54168, WO00/31061, JP-A-2001-58991, WO01/39767, WO01/39775, WO02/085291, WO02/085354, WO02/085355, WO02/085361, WO00/27815, WO00/06545, WO99/59997, WO99/48492, WO02/26714, etc.).
On the other hand, the circadian rhythm sleep disorder is a disease in which a person's main complaint or cardinal symptom is the lack of normal sleep at night, and this disease may sometimes disturb ordinary social behavior. This disease includes a variety of pathological states, for example, endogenous chronic syndromes such as delayed sleep phase syndromes caused by a disruption of the biological clock and its synchronizing mechanism, as well as exogenous acute syndromes such as jet-lag syndromes and a shift-work sleep disorder. Although various drug therapies have been tried for the treatment of circadian rhythm sleep disorder, it has been revealed that only an insufficient therapeutic effect can be obtained with hypnotics, which are typically benzodiazepine hypnotics (as a Review of pathologic states, therapy or others for a circadian rhythm sleep disorder, see, for example, S. Ozaki and K. Okawa, “Sleep Disorder and Biological Rhythm”, Special feature; Chronopharmacology, New Guideline of Administration, Molecular Medicine, Vol. 34(3), pp. 355-365, 1997, etc.).
Entrainment factors of circadian rhythm are classified into the two major groups of light (photic entrainment) and other factors than light (non-photic entrainment). The drugs which have been known to cause non-photic entrainment so far, are serotonin agonists, benzodiazepine hypnotics, melatonin and the like, but no ORL-1 receptor agonist has been reported to cause non-photic entrainment. One paper has disclosed that a small amount of nociceptin, an endogenous ligand of the ORL-1 receptor, was injected into suprachiasmatic nucleus, biological clock of hamster, but the paper has concluded that nociceptin inhibits photic entrainment, but nociceptin itself does not cause non-photic entrainment (J. Neurosci., Vol. 19(6), pp. 2152-2160, 1999).
In addition, the above-mentioned publications and the patent publication neither disclose nor suggest that a compound having an agonistic and/or antagonistic activity for the ORL-1 receptor, can be used for treating a circadian rhythm sleep disorder.